(1) Field of the Invention
The present invention relates to a semiconductor memory card for storing digital contents, and a data reading apparatus for reading out the digital contents from the semiconductor memory card. More particularly, the present invention relates to a semiconductor memory card and a data reading apparatus suitable for copyright protection of digital contents.
(2) Description of the Prior Art
The multimedia network technology has developed to the extent that digital contents such as music contents are distributed via a communication network such as the Internet. This makes it possible to access a variety of music or the like provided from around the world at home. For example, a music content can be downloaded into personal computer (hereafter referred to as PC), then stored in a semiconductor memory card loaded into the PC. Also, the semiconductor memory card can be removed from the PC and can be loaded into a portable music player. This enables one to listen to the music while walking. The semiconductor memory cards are compact and lightweight cards containing a nonvolatile semiconductor memory (e.g., a flash memory) and having a large storage capacity.
In such a music distribution, the digital contents to be stored in the semiconductor memory card need to be encrypted beforehand using a key or the like to prevent unauthorized copying of the digital contents. Also, an arrangement is required so that file management software programs, many of which are standard equipment on commercial PCs, cannot copy the digital contents to other storage mediums.
In one possible method for preventing unauthorized copying, only dedicated software programs are allowed to access the semiconductor memory card. For example, when an authentication process between a PC and a semiconductor memory card has completed affirmatively, a PC is allowed to access the semiconductor memory card; and when the authentication process has not completed affirmatively due to the lack of a dedicated software program, the PC is not allowed to access the semiconductor memory card.
However, in the above method in which PCs should always have a dedicated software program to access the semiconductor memory card, free data exchange with users via the semiconductor memory card is not available. As a result, the above method loses a merit of conventional semiconductor memory cards, namely, a merit that file management software programs being standard equipment on commercial PCs can be used to access the semiconductor memory card.
Semiconductor memory cards that can only be accessed through dedicated software programs are superior as storage mediums for storing digital contents since such semiconductor memory cards function to protect copyright of the digital contents. However, the semiconductor memory cards have a problem that they cannot be used as auxiliary storage apparatuses in general-purpose computer systems.
It is therefore an object of the present invention to provide a semiconductor memory card that can be used as a storage medium for storing digital contents and as a storage medium for storing general-purpose computer data (not an object of copyright protection), and to provide an apparatus for reading data from the storage medium.
The above object is fulfilled by a semiconductor memory card that can be used/removed in/from an electronic device, comprising: a rewritable nonvolatile memory; and a control circuit which controls accesses by the electronic device to an authentication area and a non-authentication area in the rewritable nonvolatile memory, wherein the control circuit includes: a non-authentication area access control unit which controls accesses by the electronic device to the non-authentication area; an authentication unit which performs an authentication process to check whether the electronic device is proper, and affirmatively authenticates the electronic device when the electronic device is proper; and an authentication area access control unit which permits the electronic device to access the authentication area only when the authentication unit affirmatively authenticates the electronic device.
With the above construction, the data being an object of copyright protection can be stored in the authentication area and other data can be stored in the non-authentication area, which makes it possible to achieve a semiconductor memory card which is capable of storing both digital contents to be copyright-protected and other data together.
In the above semiconductor memory card, the authentication unit may generate a key reflecting a result of the authentication process, and the authentication area access control unit decrypts an encrypted instruction using the key generated by the authentication unit, and controls accesses by the electronic device to the authentication area in accordance with the decrypted instruction, the encrypted instruction being sent from the electronic device.
With the above construction, even if the communication between the semiconductor memory card and in electronic device is tapped, the instruction to access the authentication area has been encrypted, reflecting the result of the preceding authentication. Accordingly, such a semiconductor memory card has a reliable function to protect an unauthorized access of the authentication area.
In the above semiconductor memory card, the authentication unit may perform a challenge-response type mutual authentication with the electronic device, and generates the key from challenge data and response data, the challenge data being sent to the electronic device to check whether the electronic device is proper, and the response data being generated to show the authentication unit is proper.
With the above construction, the key is shared by the semiconductor memory card and the electronic device only when both devices affirmatively authenticate each other. Furthermore, the key changes for each authentication. This enhances the security of the authentication area since the authentication area cannot be accessed without using the key.
In the above semiconductor memory card, the encrypted instruction sent from the electronic device may include a tag field and an address field, the tag field not having been encrypted and specifying a type of an access to the authentication area, the address field having been encrypted and specifying an address of an area to be accessed, wherein the authentication area access control unit decrypts the address field using the key, and controls accesses by the electronic device to the authentication area so that an access of the type specified in the tag field is made to the area indicated by the address in the decrypted address field.
With the above construction, only the address field of the instruction is encrypted. This facilitates the decryption and the decoding of the instruction by the semiconductor memory card which receives the instruction.
The above semiconductor memory card may further comprise: an identification data storage circuit which prestores identification data which is unique to the semiconductor memory card and enables the semiconductor memory card to be discriminated from other semiconductor memory cards, wherein the authentication unit performs a mutual authentication with the electronic device using the identification data stored in the identification data storage circuit, and generates the key from the identification data.
With the above construction, in the mutual authentication process, data unique to each semiconductor memory card is exchanged. This keeps a superior security level against unauthorized decoding of the mutual authentication.
The above semiconductor memory card may further comprise: an area resizing circuit which resizes the authentication area and the non-authentication area.
With the above construction the semiconductor memory card can be used dynamically. That is, the semiconductor memory card can be used mainly as a recording medium for digital contents and can be used as an auxiliary storage apparatus in a commuter system.
In the above semiconductor memory card, the authentication area and the non-authentication area may be produced by dividing a continuous area of a predetermined size in the rewritable nonvolatile memory into two, and the area resizing circuit resizes the authentication area and the non-authentication area by changing an address marking a boundary between the authentication area and the non-authentication area.
With the above construction, the size of the authentication and non-authentication areas can be changed only by moving the boundary. This reduces the circuit size.
In the above semiconductor memory card, the area resizing circuit may include: an authentication area conversion table which shows correspondence between logical addresses and physical addresses in the authentication area; a non-authentication area conversion table which shows correspondence between logical addresses and physical addresses in the non-authentication area; and a conversion table change unit which changes contents of the authentication area conversion table and the non-authentication area conversion table in accordance with an instruction from the electronic device, wherein the authentication area access control unit controls accesses by the electronic device to the authentication area by referring to the authentication area conversion table, and the non-authentication area access control unit controls accesses by the electronic device to the non-authentication area by referring to the non-authentication area conversion table.
With the above construction, it is possible to separately manage the authentication area and the non-authentication area in terms of the area size and relationships between the logical addresses and physical addresses since conversion tables for these areas are independently operated.
In the above semiconductor memory card, an area addressed with higher physical addresses and an area addressed with lower physical addresses both constituting the area having the predetermined size may be respectively allocated to the authentication area and the non-authentication area, the non-authentication area conversion table shows correspondence between logical addresses arranged in ascending order and physical addresses arranged in ascending order, and the authentication area conversion table shows correspondence between logical addresses arranged in ascending order and physical addresses arranged in descending order.
With the above construction which enables the logical addresses to be used in ascending order, the area size can be changed easily since the probability of use of an area around the boundary between the authentication area and the non-authentication area becomes low. This also lowers the probability of occurrence of data saving or moving which is required to move the boundary, resulting in a simplified area size change.
The above semiconductor memory card may further comprise: a read-only memory circuit which prestores data.
With the above construction, the function of copyright protection is enhanced by storing identification data of the semiconductor memory card in the dedicated memory and storing the digital contents depending on the results of identification based on the identification data.
In the above semiconductor memory card, each of the authentication area and the non-authentication area may include: a read/write storage area from/to which the electronic device can read/write data; and a read-only storage area from which the electronic device can read data but to which the electronic device cannot write data, the control circuit further includes: a random number generator which generates a random number each time the electronic device writes data to the rewritable nonvolatile memory, and each of the authentication area access control unit and the non-authentication area access control unit encrypts data using the random number, writes the encrypted data to the read/write storage area, and writes the random number to the read-only storage area.
With the above construction, unauthorized attempts such as tampering of the read/write storage area can be deleted by checking the compatibility with the random number stored in the read-only storage area. This enhances the safety of data writing.
In the above semiconductor memory card, the control circuit further may include: a conversion table which shows correspondence between logical addresses and physical addresses in each of the authentication area and the non-authentication area; and a conversion table change circuit which changes contents of the conversion table in accordance with an instruction from the electronic device, and the authentication area access control unit and the non-authentication area access control unit control accesses by the electronic device to the authentication area and the non-authentication area, respectively, by referring to the conversion table.
With the above construction, even if the plurality of logical blocks constituting the same file are fragmented, they can be easily changed to become logically successive. This increases the speed of accessing the same file.
In the above semiconductor memory card, the control circuit may further include: an encryption/decryption unit which encrypts data to be written to the authentication area and the non-authentication area and decrypts data read out from the authentication area and the non-authentication area.
With the above construction, it is possible to defend the authentication area and the non-authentication area against unauthorized attacks such as destroying the semiconductor memory card and directly reading the contents of these areas.
In the above semiconductor memory card, the nonvolatile memory may be a flash memory, and the control circuit further includes: a not-deleted list read unit which, in accordance with an instruction from the electronic device, identifies not-deleted areas in the authentication area and the non-authentication area, and sends information indicating the not-deleted areas to the electronic device.
With the above construction, the electronic device can identify not-deleted areas and delete the identified not-deleted areas before the flash memory is rewritten. This increases the speed of the rewriting.
In the above semiconductor memory card, the authentication unit may request a user of the electronic device to input a user key, which is information unique to the user, during the authentication process, and the control circuit further includes: a user key storage unit which stores the user key; an identification information storage unit which stores a piece of identification information identifying an electronic device that has been affirmatively authenticated by the authentication unit; and a user key request prohibition unit which obtains a piece of identification information from a target electronic device after the authentication unit starts the authentication process, checks whether the piece of identification information obtained from the target electronic device has already been stored in the identification information storage unit, and prohibits the authentication unit from requesting a user of the electronic device to input a user key when the piece of identification information obtained from the target electronic device has already been stored in the identification information storage unit.
With the above construction, the user need not input a password or personal data each time the user accesses the semiconductor memory card. This prevents the occurrence of unauthorized tapping and using of the personal data.
The above object is also fulfilled by a data reading apparatus for reading out a digital content from the above semiconductor memory card, the digital content having been stored in the non-authentication area of the semiconductor memory card, and information indicating the number of times the digital content can be read out being prestored in the authentication area, the data reading apparatus comprising: a judgement means for, when the digital content is to be read out from the non-authentication area, reading out the information indicating the number of times the digital content can be read out from the authentication area, and judging whether the digital content can be read out based on the number of times indicated in the information; and a reproduction means for reading out the digital content from the non-authentication area only when the judgement means judges that the digital content can be read out, and reducing the number of times the digital content can be read out in the information stored in the authentication area.
With the above construction, it is possible to limit the number of times the digital content is read out from the semiconductor memory card. This enables the present invention to be applied to chargeable, rental music contents.
The above object is also fulfilled by a data reading apparatus for reading out a digital content from the above semiconductor memory card and reproducing the read-out digital content as an analog signal, the digital content, which an be reproduced as an analog signal, having been stored in the non-authentication area of the semiconductor memory card, and information indicating the number of times the digital content can be initially output by the electronic device having been stored in the authentication area, the data reading apparatus comprising: a reproduction device operable to read out the digital content from the non-authentication area and reproduce the read-out digital content as an analog signal; a judgement device operable to read out the information indicating the number of times the digital content can be digitally output by the electronic device, and judge whether the digital content can be digitally output based on the number of times indicated in the information; and a digital output device operable to digitally output the digital content only when the judgement device judges that the digital content can be digitally output, and reduce the number of times the digital content can be digitally output in the information stored in the authentication area.
With the above construction, it is possible to limit the number of times the digital content is digitally copied from the semiconductor memory card. This provides a copyright protection detailed with caution and attentiveness as intended by the copyright owner.
As described above, the present invention is a semiconductor memory card functioning with flexibility both as a recording medium for storing digital contents and an auxiliary storage apparatus of a computer. The pr sent invention especially secures healthy distribution of digital contents for electronic music distribution. This is practically valuable.